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The continuation record only contained one field, xl_rem_len, so it makes things simpler to just include it in the WAL page header. This wastes four bytes on pages that don't begin with a continuation from previos page, plus four bytes on every page, because of padding. The motivation of this is to make it easier to calculate how much space a WAL record needs. Before this patch, it depended on how many page boundaries the record crosses. The motivation of that, in turn, is to separate the allocation of space in the WAL from the copying of the record data to the allocated space. Keeping the calculation of space required simple helps to keep the critical section of allocating the space from WAL short. But that's not included in this patch yet. Bump WAL version number again, as this is an incompatible change.
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Changes between all PostgreSQL releases are recorded in the file HISTORY. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.